High-frequency signaling



H. J. VAN DER BIJL. HIGH FREQUENCYSIGNALING. APPLXCAIION man AUG.2I. 1 15.

1, 350,752. Patented Aug. 24, 1920.

Fig.1 1 H42 VV/fneases: Im en/ar:

e Hendrik J van der Bf Z 3 y (3M invented certain new and useful Improve-- UNITED STATES PATENT OFFICE.

HENDRIX JOHANNES VAN DER BIJ L, OF NEW YORK, N. Y., ASSIGNOR, BY MESNE ASSIGNMENTS, TO WESTERN ELECTRIC COMPANY, INCORPORATED, A COB- IPOBLTION OF NEW YORK.

HIGH-FREQUENCY SIGNALING.

Specification of Letters Patent.

Application filed August 21, 1915. Serial No. 46,648.

To all whom it may concern:

Be it known that I, HENDRIK JOHANNES VAN DER BIJL, a subject of the Kin of Great Britain, residing at New York, in t e county of New York and State ofNew York, have ments in High-Frequency Signaling, of which the following is a full, clear, concise, and exact description.

This invention relates to signaling by high frequency electrical oscillations or waves along wires or through space, and more particularly it relates to a system for modulating high frequency oscillations in accordance with the frequency and amplitude variations of message waves to be transmitted, and its object is to effect this modulation I without destroying the quality characteristics of the message wave.

The invention provides for modulating feeble high frequency oscillations by impressing the currents of tele honic frequencies, together with the high requency oscillations, on the input circuit of a thermionic amplifier; and makes use of the fact that the amplification of a thermionic amplifier of the audion type depends upon the voltage impressed upon the grid or input circuit. If the amplifying power of the 'tube for the .high fre uency oscillations is caused to vary in aecor ance with the variations of the electromotive force of the telephonic waves of low frequency, the desired modulation is obtained, for there will be produced a high frequency wave the envelop of which is an accurate re reduction of the telephonic wave, and t is wave may then be further amplified to any required degree for effective radiation from an antenna. I

Thiswill be better understood by refer- :ence to the accompanying drawing, in which accurate picture of the low Figure 1 shows the characteristic curve of a thermionic amplifier of the audion type; Fig. 2 illustrates the form of current curve in the output circuit; Fig. 3 the' tem'; and

current curve in the radiating Fig. 4 shows an arrangement o apparatus to obtain the desired results. j

Perfect modulation refers to such a variation in the amplitude of envelop of the high frequency wave that this envelop is an lating wave;

frequency modu- According to the present invention, the max1mum negative value of the low frequency input wave is made just sufficient to reduce the modulated high frequency oscillations to zero amplitude. In other words, the icture of the low frequency oscillations, as s own in the envelop of the high frequency oscillations, just comes down to the zero line, having none of the picture out off by this zero line.

The process of modulation will be made more evident by a consideration of the characteristic curve shown in Fig. 1, which gives the relation between the output current and the input voltage of the type of amplifier used. In this curve the abscissae represent the input voltage and the ordinates represent the output current.

If we consider the effect at two different points, C and F, of adding equal positive voltages, CD and FG, on the grid, it is clear that the increase in space current by these equal increments in grid voltage is considerabl greater at F than it is at C. The amli .Now suppose that the line CD, or the e ual line F represents a small increment 'o the high frequency1 voltage, while the Patented Aug. 24,.1920.

cation will then be greater at F than at amplification of the high frequency will be increased as the potential at which the grid is maintained by the low frequency is increased from point C toward the point F of the figure.

If we suppose the normal grid voltage, when neither high frequency nor low frequency input is applied, to be such that the space current is given b AM, then when the low frequency is a plie assuming it to have equal positive an negative values, the line represent space current will be moved ual horizontal distances from both sides of and the amplifiqttion' at an instant willdepend uponthe t ofthe meteristie at which the mp is working; that is, upon the form of the low fmquencyvoltage curve, and will in fact be proportional to the of the characteristic at the point i new, highoscillations are also impressed upon the grid circuit, the high frequency current in the output circuit will depend in magnitude upon the amount of amplification, that is, upon the part of the characteristic at which the amplifier is working and therefore upon the form of the low frequency voltage curve.

Theoretically, for perfect modulation the low frequency should be large compared with the high frequency input to the modu lator, in order that the amplifying power shall not change appreciably due to the high frequency oscillations, but shall be subject to the low frequency voltage only. From a theoretical standpoint the best value for the ratio is infinity, but of course this is not practical, and it has been found that a sufficiently good modulation can be secured if the low frequency voltage input is from three to ten times as large as the high frequency voltage input.

Perfect modulation further-requires that the characteristic curve be parabolic, in which case the space current will be proportional to the square of the input voltage, as measured from B. Under these conditions the slope of the curve, which is a measure of the amplifying power, increases linearly from the point B to the point L. Under these conditions, the current in the output circuit of the modulator will have the form shown in Fig. 2 when a sinusoidal low frequency is impressed.

When the low frequency has been dropped out as the energy is passed along through an oscillation' transformer, which transmits efficiently only the high frequency output of the modulator, there will remain a high frequency current of the form shown in Fig. 3, the dotted line showing the axis of the sinusoidal envelop of the high frequency oscillations.

In view of the above it has been found desirable to generate high frequency carrier waves of a power commensurate with, or at least not greater than, that of the low frequency signaling waves to be transmitted. Where the signal waves are of low inten sity, as is the case where a commercial transmitter is their source, it followsthat the generated oscillations should be of an equally low, or lower intensity-in order that they may be effectively modulated by the telephone currents.

The arrangement of apparatus which I have found useful for the desired purpose will be clearly understood by reference to Fig. 4, in which A is a thermionic amplifier comprising an evacuated vessel 2 which incloses the cathode 3, anode 4 and an auxiliary electrode 5. Cathode 3 is heated to incandescence by the battery 6 and is maintained positive with respect to electrode 5 by means of battery 7. The normal potential of the grid is therefore at some such point as M in Fig. 3, such that the most negative grid potential resulting from the low frequency modulating wave will be just suflicient to carry the space current to zero as at point B. The space current flowing bet-ween cathode 3 and anode 4 may be supplied from a direct current generator 8 having in shunt with it a condenser 9 sufficiently high in capacity to afford a path of low impedance for both the low and high frequency currents. The input circuit of the amplifier A includes the cathode 3, battery 7, potentiometer 10, secondary 11 of the oscillation transformer 12 and the electrode 5. The primary 13 of transformer 12 is connected to a high frequency generator 14, which may be of any suitable type, such, for example, as that described in an application of Hartley, Serial No. 31,476, filed June 1, 1915. A telephone transmitter 15 is connected in series with a battery 16 in the primary circuit of a transformer 17, whose sec ondary is connected to the potentiometer 10 in the input circuit of the amplifier. The output circuit of the amplifier includes the anode 4, Winding 18 of the oscillation transformer 19, the condenser 9 and generator 8 in parallel, and the cathode 3.

In the absence of any telephonic impulses, the arrangement described serves simply to produce in this output circuit high frequency currents having substantially the same wave form as that produced by the generator 14, but of greater amplitude.

When. however, telephonic electromotive forces are impressed on the input circuit by means of the transformer 17, the electrode 5 will be made more or less negative with respect to the cathode 3, as the telephonic wave fluctuates from a negative to a positive value. This variation in the potential of the electrode 5 has the effect of varying the amplifying power of the amplifier in accordance with variations in the telephonic electromotive forces. Since the amplification produced by the tube depends upon the relative values of the internal resistance of the tube and the external impedance into which it works, it may be considered that the variation in the potential of the electrode 5 has the effect of varying the impedance of the electron discharge path between cathode 3 and anode 4, and as this path is included in the output circuit of the amplifier, it follows that the impedance of the output circuit is varied in accordance with variations in the telephonic electromotive forces. Thus, there will be produced in the winding 18 of the transformer 19 a high frequency current whose amplitude varies with the variation in amplitude of the impressed telephonic electromotive force, that is. the envelop of the high frequency wave will be an accurate reproduction of the telephonic wave.

Since it is desirable that the power value of the impressed telephonic wave shall be greater than that of the generated high frequency oscillations, it will. appear that the power value of the modulated high frequency waves produced in the transformcr 19.may Well be insufiicient for effective radiation from an antenna. In such case the power may be amplified to the degree required for radiation by means of some such arrangement as that described in patent to Arnold No. 1,129,942, March 2. 1915. ()n the other hand, it may well be that the high frequency oscillations have a fairly large power to start with. and in this case it may be necessary to amplify the telephonic power before impressing the two upon a common amplifier.

It has been found desirable to have the external impedance of the output circuit fairly small in order that the characteristic curve of the amplifier shall not be materially altered as the current in the output circuit changes.

\Vhile in the present instance the transformer 17 is shown directly connected to a telephone transmitter 15, it is to be understood that this transformer may be connected to a telephone line and serve as a means for relaying. to a wireless antenna or other high frequency signaling system, telephonic or other messages received over long distance conductors. It is also evident that the arrangement shown is suitable for telegraphic transmission by simply substituting a telegraph key for the transmitter 15 and adding an interrupter of any desired frequency. It is evident also that although this invention is particularly well adapted for use in signaling systems, which constitutes the principal application for modulated currents. in its broader aspects the invention may be used wherever it is desired to modulate waves or periodic disturbances, regardless of the use which is to be made of the modulated current or the medium in which the disturbances are produced.

hat is claimed is:

1. The method of modulating carrier waves which consists in generating carrier waves of substantially constant amplitude. and invariably amplifying the amplitude of said carrier waves in accordance with a signal.

2. The method of modulating carrier current which comprises generating a high frequency carrier wave of substantially constant amplitude, simultaneously 'generating a low frequency wave and variably amplifying the high frequency wave in accordance with said low frequency wave.

3. The method of modulation which comprises generating a current of high frequency, generating a current of relatively low frequency, impressing energy from each of these currents in series upon a circuit, generating space current and causing the energy impressed upon said circuit to vary said space current, said variations being of the frequency of said carrier current but having greater amplitudes, the amplification varying in accordance with the varia-' tions of said low frequency current.

4. The method of modulating a high frequency carrier current by means of a space discharge amplifier having an input circuit and an output circuit, the amplifying power of which varies with the energy supplied to the input circuit, which comprises generating a high frequency carrier wave, generating a low frequency wave, and impressing said high frequency wave and said low frequency wave simultaneously and in series upon the input circuit of the amplifier.

5. The method of modulating high frequency carrier current which consists in producing a high frequency carrier wave, simultaneously producing a low frequency wave of greater amplitude than said high frequency Wave and variably amplifying said high frequency wave in accordance with said low frequency wave.

6. The method of modulation which consists in generating a high frequency wave, simultaneously generating a low frequency wave having an amplitude at least as great as that of said high. frequency wave and variably amplifying said high frequency wave in accordance with said low frequency wave.

7. The method of operating a thermionic amplifier having a cathode, an anode, a space current control means, input and output circuits and a source of space current in said outputcircuit, which method comprises simultaneously impressing upon said control means a series of high frequency waves and a series of low frequency waves and a constant potential, and so adjusting the apparatus that the space current in said output circuit periodically falls to substantially zero value.

8. The method of signaling which comprises generating a series of waves and subsequently simultaneously amplifying and modulating each of the waves in accordance with a signal.

9. In a system for radio-transmission, a source of high frequency oscillations. an amplifier having an input circuit and an output circuit, means for impressing said high frequency oscillations on said input circuit, a primary source of low frequency currents, and a path of variable impedance in said output circuit controllable by said low frequency currents.

10. In a system for radio-transmission, a source of high frequency oscillations, an amplifierfor said oscillations having an input circuit, and a primary source of low frequency currents connected with said input circuit whereby the amplification of said oscillations is made to vary in conformity with variations in said low frequency currents.

11. in a system for radio-transmission, a thermionic amplifier having an input circuit, a source of high frequency oscillations connected with said input circuit, and a primary source of low frequency electromotive force also connected with said input circuit.

12. The combination with a source of low frequency currents, of a source of high frequency oscillations, means for amplifying said oscillations comprising an evacuated vessel containing an electron-emitting cathode, an anode and an auxiliary electrode, an input circuit including said cathode and said auxiliary electrode, means for impressing said oscillations on said input circuit, and a connection between said low frequency current source and said input circuit in series with said means.

13. The combination with a source of low frequency signal impulses, of a generator of high frequency oscillations, means for amplifying said oscillations comprising a thermionic repeater having an input circuit and an output circuit, a high frequency transformer having its primary connected to said generator and its secondary included in said input circuit, a low frequency transformer having its primary connected to said low frequency source and having its secondary connected to said input circuit in series with the secondary of said high frequency transformer.

14. The combination with an electric discharge device having main electrodes and an impedance controlling means, of an output circuit for said device, a source of current in said output circuit. and means for simultaneously impressing upon said controlling means high frequency waves and low frequency waves, auxiliary means for impressing a substantially constant pressure upon said controlling means, the relative magnitudes of the waves and the constant pressure being such that the discharge current periodically falls to substantially zero value at the frequency of said low fre quency waves.

15. The combination with an amplifier having the property of variably amplifying in accordance with the energy impressed thereupon, of a circuit for impressing energy upon said amplifier. means for simultaneously impressing high frequency waves and low frequency waves upon said circuit, the amplitude of said high frequency Waves being less than the amplitude of said low frequency waves.

16. The combination with an amplifier -plitude at least as great as having the property of variably amplifying in accordance with the energy impressed thcreon, of means for simultaneously impressing high frequency waves and low frequency waves upon said amplifier, said waves of low frequency having an amthat of said waves of high frequency.

.17. In a modulating system, thecombination with a source of high frequency oscillations, of means for modulating said oscillations, said means comprising a device asymmetrically conducting for said high frequency oscillations and an impedance varying clcmcnt therefor, said means being free from contact resistance.

18. The combination with a space discharge devicc, of a source of space current therefor, a source of carrier waves acting upon said device, a source of low frequency signaling waves acting upon said device, means associated with said dcvice for causing said carrier waves to impress variations of their own frequency upon said space current, and means for transforming said variable current into alternating current of carrier frequency modulatcd in accordance with said low frequency signaling waves.

19. The combination with a source of high frequency Waves, a source of low frequency waves, a source of space current, and means for varying an impedance presented to said space current, said means being controlled by both the high and the low frequency waves, and means whereby the effect of said high frequency waves upon the impedance presented to said space current is varied periodically by said low frequency waves.

20. In a high frequency signaling system, a source of high frequency oscillations. and a power amplifier having a curved characteristic for modulating and amplifying said oscillations in accordance with a signal.

21. In a transmission system, a source of high frequency oscillations, power amplifying means for modulating said oscillations and means for impressing said high frequency oscillations upon said amplifying means, the amplifying power of said means being substantially independent of the amplitude of the impressed high frequency oscillations.

22. In a modulating system, the combination with a source of high frequency oscillations, of means for modulating said oscillations, said means comprising a space discharge device and an impedance varying clement therefor, said means being free from contact resistance.

23. The combination with an electric discharge device having main electrodes and an impedance-controlling means, of an input circuit and an output circuit each connected to said device, a source of high frequency fying power substantially proportional to the amplitude of the impressed low fre-- quency' electromotive force.

24. The combination with *a modulator having an input circuit of high impedance, of means for impressing high frequency impulses upon said circuit; means in series with said last-mentioned means for impressing low frequency impulses upon said circuit, and means to reduce the impedance effect of one of said means upon the impulses impressed upon said circuit by the other of said means.

25. The combination with a modulator having an input circuit of high impedance, of a transformer for impressing; high frequency impulses upon said circuit, a second transformer in series with said first-mentioned transformer for impressing low frequency impulses upon said circuit, a resistance element in series with said transformers in saidcircuit, and a second resistance element in parallel circuit arrangement with said first resistance element and one of said transformers.

26. In a system of communication, a generator providing a source of high frequency oscillations, a source of signal oscillations, an asymmetrically conducting thermionic device having a constantly active source of electrons, an input circuit and an output circuit, means for impressing oscillations from both of said oscillation sources upon the input circuit of said thermionic device, and a high frequency transmission circuit associated with the output circuit of said device.

27. The method of producing modulated waves, which comprises producing a carrier wave, amplifying said carrier wave and simultane'ously varying the amplification of said carrier wave so as to make it substantially proportional to the amplitude of a low frequency wave.

28. The method of producing modulated waves which comprises producing a carrier wave, amplifying said carrier wave and simultaneously controlling the amplification of said carrier wave substantially exclusively in accordance with slow. frequency wave.

29. The method of producing modulated waves which comprises impressing a carrier wave upon an amplifier to produce an amplified carrier wave and simultaneously impressin u on said amplifier another wave of muc arger amplitudethan said impressed carrier wave in order to control the l-magnitude of the amplified carrier 4r wave.

the amp 30. The method which comprises simultaneously subjecting a thermionic device having a variable amplifying power to the action of a high frequenc wave, and a low frequency wave, the ampiitude of the high frequency wave being insufiicient to cause considerable chan e in the amplifying power of said amp ifier and the amplitude of the low frequency wave being suflicient to cause lar e change in the amplifying.

power of sai amplifier. I

31. The method of operating a thermionic discharge device having a cathode, an anode and an impedance control element, an input circuit connected to said cathode and said impedance control element and an output circuit connected to said cathode and said anode, which method comprises impressing a high frequency electromotive force upon said input circuit, simultaneously impressing an electromotive force between said control element and said cathode, negatively directed with respect to said control element, and varying at a low fre uency rate the effective value of said negatively directed electromotive force.

32. The method of producing a 'modu- .lated wave which comprises impressing a carrier wave upon a thermionic amplifier having .a curved characteristic and simultaneously impressing upon said amplifier an electromotive force varying at a low frequency and of a magnitude within a range throughout which the curved characteristic is substantially parabolic.

33. In combination, means for producing a carrier wave, means connected thereto for amplifying said carrier wave, means for producing a low frequency wave connected to said amplifying means and means associated therewith whereby the amplification of said carrier wave may be made substantially proportional to the amplitude of said low frequency wave.

34. In combination, means for producing a carrier wave, means connected thereto for amplifying said carrier wave, means connected to said amplifying means for controlling the am lification of said carrier wave substantial y exclusively in accordance with a low frequency wave.

35. Means for producing a carrier wave an amplifier connected to said means, an means for impressin upon said amplifier another wave of amp itude large compared with that of said impressed carrier wave in order to control the magnitude of the amplified carrier wave.

36. In combination," an amplifier having a variable amplifying power, a high frequency source and a ow frequenc source, means'conneeting said sources to said amplifier to simultaneously impress thereon high frequenc waves an .low frequency waves,

'tude of the impressed high frequency Waves being insufficient to cause considerable change in the amplifying ower of said amplifier and the amplitude 0 the impressed low frequency waves being sufiicient to cause large change in the amplify ing power of said amplifier.

37. A thermionic discharge device having a cathode, an adode and an impedance control element, an input circuit connected to said cathode and said control element, an out ut circuit connected to said cathode an anode, a high frequency source connected to said input circuit, means for impressing a negative electromotive force upon said controlelement with respect to said cathode, and means for varying at a low 38. In combination, a thermionic ampli- 'fier having a curved characteristic, means for impressing thereon a carrier wave, means for simultaneously impressing upon said amplifier an electromotive force varying at low frequency andflhaving an amplitude within a range throughout which said curved characteristic is substantially parabolic.

In witness whereof, I hereunto subscribe my name this 20th day of August, A. D., 1915.

HENDRIK JOHANNES VAN DER BIJL.

Corrections in Letters Patent No. 1,350,752.

It is hereby certified em in 1mm Patent No. 1,350,752, granted August 24, 1920, upon the application of Hendrik Joha mnes van der Bijl, of New York N Y J for enimprovement in High-Frequency fiignflling," errors appear i h primod specification requiring correction as follows: Page 3, line 53, claim 1, for th wi "inve riably toad in vgriably (five words); page 6; line 8, diiiiiemor adode read anode; and that the'said Letters Patent should be mad Eh these corrections therein that the some may conform to the recoi-d of the case in the Patent Ofiice. J

Signed endffleslod this 30th 0 November, A D., 1920.

sun] L.- B; mum,

Acting Commissioner of Patents. (:1. 177-171. I e 

